Europe's Herschel and Planck telescopes have blasted into space on an Ariane 5 rocket from Kourou in French Guiana, to help unlock some of the secrets of the Universe.
Astronomers and other scientists from Cardiff University have played a key role in their development, building key parts for both satellites and creating the experiments and tests that will be conducted.
Gemma Ryall joined them at the university as they watched the rocket launch via a live link-up with the South American spaceport.
As the countdown to lift-off started, you could hear a collective intake of breath.
This was the moment many in the room had been working towards for 15 years.
The scientists at Cardiff University's School of Physics and Astronomy knew all too well what was at stake as the Herschel and Planck telescopes were blasted into space on an Ariane 5 rocket.
If the launch was successful, they could be part of unlocking more secrets of the Universe.
If it went wrong, all their years of painstaking research and work - plus around 1.9bn euros (£1.7bn) - would be blown apart, quite literally.
As astrophysicist Peter Hargrave put it: "There's an 85% chance of success. But that still means there's a 15% chance that 15 years of your life will go up in smoke.
"But at times like this you just have to put your faith in science and engineering and hope everyone's done their maths right."
Those watching the launch were tense and nervous
The team at Cardiff University know all about putting their faith in science.
For years they have been building components that will help the two satellites probe deeper into the Universe than ever before.
The Herschel telescope will be sensitive to far-infrared and sub-millimetre (radio) wavelengths of light, allowing it to peer through clouds of dust and gas to see stars at the moment they are born.
This infrared capability will also enable Herschel to look deep into space, to gaze at those galaxies that thrived when the universe was roughly a half to a fifth of its present age.
It is hoped that they will then gain a better understanding of how stars and galaxies evolve and, in turn, give them a greater insight into our own Sun and Solar System.
Key to this is the Spire (Spectral and Photometric Imaging Receiver) instrument, which has been designed and built by a Cardiff-led consortium of 18 institutes in eight countries.
Cardiff's teams have helped build parts for both Herschel and Planck
It will be able to detect one million, million, millionth of the brightness of a 60W lightbulb, according to Cardiff's Prof Matt Griffin, who leads Spire's consortium.
The other satellite, Planck, although being launched at the same time as Herschel, will carry out a different task.
It will make the finest ever measurements of what has become known as the Cosmic Microwave Background (CMB) - the "oldest light" in the universe. It is all around us and comes from a time 380,000 years after the Big Bang.
Key parts were built by another consortium including a team at Cardiff University.
Once they are both in orbit, Cardiff's scientists will help operate the instruments and conduct tests and experiments over the next three to four years.
So, as the rocket blasted off, it was clear just how much a successful launch meant for the university and its dedicated staff.
The rocket carried the satellites for half an hour before they separated
As the rocket powered into the blue sky above French Guiana, there were no cheers, no popping of champagne corks, like I had expected.
There was still the small - but crucial - matter of the separation of the two satellites from the rocket, which would happen about half an hour after lift-off.
As the room collectively mumbled tensely, waiting for that key moment, Prof Steve Eales said: "I woke up at 4.15am this morning, I was so nervous. Some people have spent 10 years and more on this. I've only been involved for a few years but I felt sick to the stomach."
Then - finally - we had the cheers.
As the link-up showed the satellites had broken away from the rocket and had successfully started their own journey across space, the room erupted and wine started flowing.
"I'm so relieved and enormously proud of what we have done to get this off the ground," said Prof Eales, who will lead a team of about 110 people from universities all over the world, including the US and China in using the data received from the satellites.
Scientists were joined by First Minister Rhodri Morgan to celebrate
"If this were to have blown up, we would have been in an absolute mess. We put so much work into it. A lot of people could have lost their jobs and grants and funds coming for it would have gone."
For Prof Walter Gear, head of the school, the launch was a chance to reflect on all that had been achieved by his team.
"It's a proud moment, incredible," he said. "This is a huge deal for Cardiff University and shows how far we've come.
"I think it will attract even more students to Cardiff. Over the last few years, we have seen our recruitment of undergraduates increase. The fact we can now show our involvement in this should make it even more buoyant."
The team have a month to relax before the next key moment comes in the satellites' journeys.
After reaching their orbit at 1.5 million km from Earth on its "night side", a number of tests will be carried out to check all instruments are still functioning correctly.
If all goes to plan - and everyone has "done their maths right" - the experiments can then start. And who knows what secrets will be revealed.